1. Field of the Invention
The present invention relates to a fuel injection valve for an internal combustion engine and particularly to improvement of an electromagnetic fuel injection valve utilized in a fuel supply system in an internal combustion engine.
2. Description of the Related Art
The typical configuration of a fuel injection valve of this kind will be explained with reference to FIG. 1. As illustrated in FIG. 1, a fuel injection valve 1 is configured mainly with a solenoid device 2 and a valve device 12. The solenoid device 2 is configured with a housing 3 that is a yoke portion of a magnetic circuit, a core 4 that is a fixed iron core portion of the magnetic circuit, a coil 5 energized from outside via a connector 6, an armature 7 that is a moving iron core portion of the magnetic circuit, and a valve-closing spring 9 that biases a needle 8 coupled with the armature 7 downstream. In addition, a fuel is supplied through a fuel inlet 10 situated at the upper portion of the fuel injection valve 1, and injected through a valve seat 15; the side of the fuel inlet 10 is referred to as “an upstream side”, and the side of the valve seat 15 referred to as “a downstream side”.
In contrast, the valve device 12 is configured with a hollow body 13 that is coupled with the housing 3 and contains part of the core 4 and the armature 7, the needle 8 that is disposed inside the body 13 and coupled with the armature 7, a guide 14 that is provided at the downstream side of the body 13 and guides the slide of the needle 8, and the valve seat 15 that controls a fuel flow by detaching or attaching the needle 8 thereby opening or closing an injection nozzle 15A. The operation of the foregoing fuel injection valve 1 is well known; thus, the explanation therefor will be omitted.
The detail of the configuration of the conventional fuel injection valve 1 will be explained below with reference to FIGS. 4 to 6 each of which is a partial enlarged view of the solenoid device 2 and the valve device 12. In the typical conventional fuel injection valve 1, as illustrated in FIG. 4, the armature 7 and the needle 8 are integrated by means of welding, press fitting, or the like; the armature 7 is pressed downstream by the valve-closing spring 9. However, as described above, the typical conventional fuel injection valve 1 employs an electromagnet-driving method in which the coil 5 is energized; therefore, due to energization or de-energization of the coil 5, the armature 7 moves up and down. The vertical movement causes the armature 7 to collide with the core 4 or causes the needle 8 to collide with the valve seat 15; as a result, in some cases, the impact of the collision causes the travel members to bounce, whereby the amount of fuel injection cannot accurately be controlled.
In order to cope with the problem of bouncing, as illustrated in FIGS. 5 and 6, there is suggested a fuel injection valve in which the needle 8 and the armature 7 are separated from each other. In FIG. 5, the upstream end of the needle 8 penetrates the armature 7, and the front end of the needle 8 is fixed in a stopper 16 by means of welding or the like; on that occasion, an elastic member 17, such as a spring, is inserted between the stopper 16 and the armature 7, and the upper portion of the stopper 16 is pressed by the valve-closing spring 9 in such a way that the needle 8 and the armature 7 are pressed downstream. Because the existence of the elastic member 17 enables the armature 7 to travel in the axis direction by a predetermined amount with respect to the needle 8, an impact force caused by a collision is relaxed (e.g., refer to National Publication of International Patent Application No. 2002-506502).
Additionally, as is the case with the fuel injection valve illustrated in FIG. 5, the fuel injection valve illustrated in FIG. 6 is configured in such a way that the needle 8 and the armature 7 are separated; however, the fuel injection valve illustrated in FIG. 6 is further configured in such a way that, instead of inserting the elastic member 17, such as a spring, between the armature 7 and the stepped portion 19 of the needle 8, a predetermined gap is formed between the stepped portion 19 of the needle 8 and a bottom contact surface 21 of the armature 7 when the stopper 16 and a top contact surface 20 of the armature 7 make contact with each other.
Assuming that the armature 7 is attracted by the core 4 to collide with the core 4, the impact of the collision causes the armature 7 to rebound; however, the needle 8 tends to further travel toward the core 4, due to the inertia of its upward movement. In other words, although the respective directions of the energy of the armature 7 and the energy of the needle 8 are opposite to each other, the energy caused by the collision can be cancelled, by allowing the relative movement between the armature and the needle 8 by means of the gap between the stepped portion 19 of the needle 8 and the bottom contact surface 21 of the armature 7 (e.g., refer to Japanese Patent Laid-Open Pub. No. 2003-512557).
However, there has been a problem that the number of components and the number of processes considerably increase in such a structure, as disclosed in National Publication of International Patent Application No. 2002-506502, in which the armature 7 and the needle 8 are coupled with each other by means of the elastic member 17 such as a spring, whereby the structure becomes complex. Additionally, in the case of such a structure as disclosed in Japanese Patent Laid-Open Pub. No. 2003-512557, due to the existence of the gap between the stepped portion 19 of the needle 8 and the bottom contact surface 21 of the armature 7, the position of the armature 7 cannot be fixed; therefore, there has been a problem that the vibration of the internal combustion engine or the like causes the distance between the armature 7 and the core 4 to be unstable while the valve is closed, whereby the time required to open the valve fluctuates and the accuracy of an injection amount is deteriorated.